This invention relates to an improvement in an electrostatic reproduction machine, but more particularly to an electrostatic reproduction machine having an improved apparatus for removing background particles from a photoreceptor prior to image transfer.
In the practice of xerography as described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface, and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern or latent electrostatic image in conformity with the configuration of the original pattern.
The latent electrostatic image is developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is greatest, the greatest amount of material is deposited, and where the field is least, little or no material is deposited. Thus, a powder image is produced in conformity with the image of the original being produced. The powder image is subsequently transferred to a sheet of paper or other transfer member, and suitably affixed thereto to form a permanent copy.
The latest concept for electrostatic reproduction machines utilizes high speed flash exposure of a document, and a moving photoconductive material in the form of an endless belt which is continuously charged. Additionally, such reproduction machines are provided with a developing system which supplies toner particles in relatively large quantities for solid area coverage, such as a magnetic brush developing apparatus. Thus, after the belt passes the magnetic brush assembly, for example, a xerographic powder image is formed on the belt which corresponds to the electrostatic latent image. This powder image is then transferred to a support surface (e.g., a sheet of paper) to which it is fused by a fusing assembly whereby the powder image is caused to adhere to the support surface permanently.
The latest electrostatic reproduction machines are high speed machines which print copies at a rate substantially in excess of any previous electrostatic reproduction machines, and are intended to compete with other types of printing machines, e.g., offset printing machines. Because of this, it is desired that the quality of the copies made, be extremely high. Important to high quality copies is the removal of all or substantially all of the background particles (i.e., toner in non-image areas) from the photoreceptor before transfer of the developed image to a support member. As stated above, large amounts of toner are used in these high speed electrostatic reproduction machines to develop the latent electrostatic image, and to produce high quality copies, a very efficient background removal apparatus is necessary to remove any background particles which may be present after development. This apparatus must be superior to previous means used to reduce the background (e.g., lamps or pre-transfer corona charging devices used to prevent or reduce transfer of background particles) on copies in that it must eliminate all or substantially all of the background from the copies; the apparatus must also not detrimentally affect the developed image on the photoreceptor to any great degree as did some of the previous means.
It is also highly desirable that the life of the developer (carrier plus toner) be extended, and the life of the developer is directly related to background, the less the background, the longer the life of the developer. By efficiently removing all or substantially all of the background, developer life will be substantially increased, possibly doubled. Also, this apparatus should be integrated into a machine so as to occupy minimal space, cooperate with other elements of the machine, be accessible, and be designed for easy maintenance by the machine operator.